Molecular sabotage of host plant defenses by spider mites

Plants constitute an ample source of nutrients for a diversity of organisms that include viruses, microbes, nematodes, insects, and mites. To protect their resources, plants possess a robust immune system that establishes structural and biochemical defenses to fight invaders. Some of these defenses are highly effective but often are very costly to sustain. Thus plants have developed inducible defenses, i.e. they are only produced when needed, regulated by a highly interconnected network in which hormones and protein hubs play important roles. However, plant diseases and pest outbreaks still occur. Many successful plant parasites manipulate the regulation of their host inducible defenses, and often they do so by employing specialized secreted proteins that sabotage the plant immunity network. In phytopathology these proteins are known as effectors. In this thesis I have discovered an arsenal of effector proteins in spider mites, particularly in the saliva of two spotted spider mite (Tetranychus urticae) and the red tomato spider mite (T. evansi), both of which are problematic pests in agriculture. These small herbivores are able to suppress plant defenses, particularly those regulated by the phytohormones jasmonic acid (JA) and salicylic acid (SA), and in this thesis I postulate that spider mites likely achieve such feats by using their effector arsenal